Publication number | US7212633 B2 |

Publication type | Grant |

Application number | US 10/400,440 |

Publication date | May 1, 2007 |

Filing date | Mar 28, 2003 |

Priority date | Apr 3, 2002 |

Fee status | Lapsed |

Also published as | DE60301750D1, DE60301750T2, EP1351430A1, EP1351430B1, US20030190041 |

Publication number | 10400440, 400440, US 7212633 B2, US 7212633B2, US-B2-7212633, US7212633 B2, US7212633B2 |

Inventors | Kaoru Yokota, Motoji Ohmori |

Original Assignee | Matsushita Electric Industrial Co., Ltd. |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (5), Referenced by (5), Classifications (10), Legal Events (6) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 7212633 B2

Abstract

An expansion key generating device that receives encryption key data as input, and outputs plural expansion key data, comprising: a data dividing unit operable to divide the encryption key data into plural part key data; and plural key conversion units being connected in series, which output the plural expansion key data. Each of the plural key conversion units includes: an output calculation unit operable to receive the plural part key data or plural output data from a preceding key conversion unit as plural input data, which executes a fixed conversion process for each of the plural input data in so that each bit value of each of the plural input data does not interfere each other, and further outputs plural output data to a subsequent key conversion unit; and an expansion key calculation unit operable to combine plural input data and calculate the expansion key data.

Claims(10)

1. An expansion key generating device operable to receive encryption key data as an input and operable to output a plurality of expansion key data comprising:

a data dividing unit operable to receive the encryption key data, operable to divide the encryption key data into a plurality of part key data, and operable to output the plurality of part key data; and

a plurality of key conversion units connected in series, each operable to receive the plurality of part key data as an input, and operable to output the expansion key data, wherein each of the plurality of key conversion units includes:

an output calculation unit operable to

receive as a plurality of input data, either the plurality of part key data or a plurality of output data from a preceding key conversion unit as a plurality of input data;

execute a fixed conversion process for each of the plurality of input data such that each bit value of each of the plurality of input data does not interfere with each other, wherein said output calculation unit is operable to execute a rotation shift operation to at least one of the plurality of input data, where the bits of at least one of the plurality of input data are shifted according to a specific number; and

subsequently output a plurality of output data to a subsequent key conversion unit; and

an expansion key calculation unit operable to receive and combine the plurality of input data, and operable to generate and output the expansion key data.

2. The expansion key generating device according to claim 1 , wherein the specific number by which the rotation shift operation shifts the bits of the input data is not a measure of a number of bits of the input data.

3. The expansion key generating device according to claim 1 , wherein said output calculation unit is operable to change a position of each of the plurality of input data according to a predefined rule, after the execution of the rotation shift operation, and operable to subsequently output the plurality of output data.

4. The expansion key generating device according to claim 1 , wherein, during the process of combining the plurality of input data, said expansion key calculation unit is operable to execute a substitution process to at least one of the plurality of input data according to a specific substitution table.

5. An expansion key generating device operable to receive encryption key data as an input and operable to output a plurality of expansion key data comprising:

a data dividing unit operable to receive the encryption key data, operable to divide the encryption key data into a plurality of part key data, and operable to output the plurality of part key data; and

a plurality of key conversion units connected in series, each operable to receive the plurality of part key data as an input, and operable to output the expansion key data, wherein each of the plurality of key conversion units includes:

an output calculation unit operable to:

receive as a plurality of input data, either the plurality of part key data or a plurality of output data from a preceding key conversion unit as a plurality of input data;

execute a fixed conversion process for each of the plurality of input data, such that each bit value of each of the plurality of input data does not interfere with each other; and

subsequently output a plurality of output data to a subsequent key conversion unit; and

an expansion key calculation unit operable to:

receive the plurality of input data;

substitute at least one of the plurality of input data according to a specific substitution table;

combine the plurality of input data; and

generate and output the expansion key data,

wherein said expansion key calculation unit includes:

a first combining unit operable to combine at least two of the input data from the plurality of input data, and generate a first combined data;

a data substituting unit operable to execute a substitution process to the first combined data according to the specific substitution table, and operable to output substituted data;

a second combining unit operable to combine the substituted data and at least one of the input data from the plurality of input data, and operable to generate a second combined data; and

an expansion key generating unit operable to receive as a data input at least said second combined data, and operable to generate the expansion key data.

6. An expansion key generating device operable to receive encryption key data as an input and operable to output a plurality of expansion key data comprising:

a data dividing unit operable to receive the encryption key data, operable to divide the encryption key data into a plurality of part key data, and operable to output the plurality of part key data; and

a plurality of key conversion units connected in series, each operable to receive the plurality of part key data as an input, and operable to output the expansion key data, wherein each of the plurality of key conversion units includes:

an output calculation unit operable to:

receive as a plurality of input data, either the plurality of part key data or a plurality of output data from a preceding key conversion unit as a plurality of input data;

execute a fixed conversion process for each of the plurality of input data, such that each bit value of each of the plurality of input data does not interfere with each other;

subsequently output a plurality of output data to a subsequent key conversion unit; and

an expansion key calculation unit operable to:

receive the plurality of input data;

substitute at least one of the plurality of input data according to a specific substitution table;

combine the plurality of input data;

concatenate the result of the substitution process and the result of combining the plurality of input data; and

generate and output the expansion key data according to the concatenation result.

7. An encryption device operable to encrypt plain text data using encryption key data comprising:

an expansion key generating device operable to receive encryption key data as an input, and operable to output a plurality of expansion key data; and

a data scrambling device operable to encrypt the plain text according to the plurality of expansion key data output by said expansion key generating device, and operable generate and output ciphertext data;

wherein said expansion key generating device includes:

a data dividing unit operable to divide the encryption key data into a plurality of part key data, and operable to output the plurality of part key data; and

a plurality of key conversion units connected in series, each operable to receive the plurality of part key data as an input, and operable to output the expansion key data, wherein each of said plurality of key conversion units includes:

an output calculation unit operable to:

receive as a plurality of input data either the plurality of part key data or a plurality of output data from a preceding key conversion unit;

execute a fixed conversion process for each of the plurality of input data such that each bit value of each of the plurality of input data does not interfere with each other, wherein said output calculation unit is operable to execute a rotation shift operation to at least one of the plurality of input data, where the bits of at least one of the plurality of input data are shifted according to a specific number; and

subsequently output a plurality of output data to a subsequent key conversion unit; and

an expansion key calculation unit operable to receive and combine the plurality of input data, and operable to generate and output the expansion key data.

8. The encryption device according to claim 7 , wherein the specific number by which the rotation shift operation shifts the bits of the input date is not a measure of a number of bits of the input data.

9. A decryption device operable to decrypt ciphertext data using encryption key data comprising:

an inverse expansion key generating device operable to receive encryption key data as an input, and operable to output a plurality of expansion key data in the reverse order of an expansion key generating device; and

an inverse data scrambling device operable to decrypt the ciphertext data according to the plurality of expansion key data output by said inverse expansion key generating device, and operable to generate and output decryption text;

wherein said inverse expansion key generating device includes:

a key modification unit operable receive the encryption key data, operable to divide the encryption key data into a plurality of part key data, operable to arrange the position of each of the plurality of part key data according to a predefined rule, and operable to subsequently output the plurality of part key data; and

a plurality of inverse key conversion units connected in series, each operable to receive as a plurality of input data either the plurality of part key data output from said key modification unit or a plurality of output data from a preceding inverse key conversion unit, operable to generate the expansion key data in a reverse order of the expansion key generating device, and operable to output data to a subsequent inverse key conversion unit, wherein each of said plurality of inverse key conversion units includes:

an output calculation unit operable to:

receive the plurality of input data received by said inverse key conversion unit;

execute a fixed conversion process for each of the plurality of input data such that each bit value of each of the plurality of input data does not interfere with each other, wherein said output calculation unit is operable to execute a rotation shift operation to at least one of the plurality of input data, where the bits of at least one of the plurality of input data are shifted according to a specific number; and

subsequently output a plurality of output data to a subsequent inverse key conversion unit; and

an expansion key calculation unit operable to receive and combine the plurality of input data, and operable to generate and output the expansion key data.

10. The decryption device according to claim 9 , wherein the specific number by which the rotation shift operation shifts the bits of the input data is not a measure of a number of bits of the input data.

Description

(1) Field of the Invention

The present invention relates to an encryption system. More specifically, the present invention relates to an encryption system which has a decreased difference between encryption time and decryption time, and is capable of generating a highly random expansion key.

(2) Description of the Related Art

Due to a rapid spread of digital communication in recent years, a data encryption method for securing data confidentiality through communication is highly demanded for the purpose of protecting privacy and the development of sound industries. In order to realize an encryption method, a speedy encryption process, and easy implementation, and a high security level are required. In a generic structure of such an encryption method, the data subject for encryption is divided into blocks of a specific size, a data scrambling process is executed to each block based on a specific encryption key, and then a ciphertext is generated.

(First Related Art)

As one of such encryption methods, there is Rijndael encryption which is established as the Advanced Encryption Standard (AES). The AES is the next generation standard of encryption in the United States. **1300** includes an expansion key generating unit **6** that generates and outputs 128-bit expansion keys SK**0**˜SK**10** from a 128-bit encryption key EK, and a data scrambling unit **5** that is connected to the expansion key generating unit **6**. The data scrambling unit **5** receives the expansion keys SK**0**˜SK**10** from the expansion key generating unit **6**, executes a data scramble by repeating a specific data conversion process for a plain text PT of 128-bit data using the expansion keys SK**0**˜SK**10**, and generates a 128-bit ciphertext CT.

The expansion key generating unit **6** includes the following elements: a data dividing unit **600** that receives the encryption key EK, divides the encryption key EK into four 32-bit data blocks D**0**, D**1**, D**2** and D**3**, and outputs them; a key conversion unit **60** that is connected to the data dividing unit **600**, receives the data blocks D**0**˜D**3** from the data dividing unit **600**, executes a specific operation, which is explained later, to them, and generates the expansion key SK**1** and four 32-bit data blocks, and outputs them; and key conversion units **61**˜**69**, each of which is connected to the preceding key conversion unit, receives four 32 bits data blocks from the key conversion unit, executes a specific operation, which is explained later, to them, generates the expansion key and four 32-bit data blocks, and outputs them.

The expansion keys output from the key conversion units **61**˜**69** are defined as the expansion keys SK**2**˜SK**10** respectively. Although the key conversion unit **69** outputs four data blocks, they are not used for other processes. In addition, the expansion key generating unit **6** outputs the encryption key EK as the expansion key SK**0**.

The data scrambling unit **5** includes the following elements: a key adding unit **500**, which is connected to the expansion key generating unit **6**, where the key adding unit **500** receives the expansion key SK**0**, executes an exclusive-OR operation per bit between a plain text PT and the expansion key SK**0**, a data conversion unit **50** connected to the key adding unit **500** and the key conversion unit **60** which converts the data output from the key adding unit **500** based on the expansion key SK**1**; data conversion units **51**˜**58** which are connected to the key conversion units **61**˜**68** respectively, and convert the data output from the preceding data conversion unit based on the expansion keys SK**2**˜SK**9** respectively; and a final data conversion unit **59**, which is connected to the data conversion unit **58** and the key conversion unit **69**, where the final data conversion unit **59** converts the data output from the data conversion unit **58** based on the expansion key SK**10**, and outputs a ciphertext CT.

**60**˜**69**. Each of the key conversion units **60**˜**69** executes a key conversion process, which is explained later, based on first˜fourth input data X**0**˜X**3** of 32 bits each, and outputs first˜fourth output data Y**0**˜Y**3** and the 128-bit expansion key SK.

Each of the key conversion units **60**˜**69** includes the following elements: a data rotation unit **601** that receives the fourth input data X**3**, executes a rotation bit shift by 8 bits to the input data X**3** in an upper bit direction (a left direction), and outputs its result; a data substituting unit **602** that is connected to the data rotation unit **601**, receives the operation result from the data rotation unit **601**, executes a specific substituting process to the operation result, and outputs its result; and an exclusive-OR operation unit **603**, which is connected to the data substituting unit **602**, where the exclusive-OR operation unit **603** receives the substitution result from the data substituting unit **602**, executes the exclusive-OR operation per bit between the substitution result and a predefined 32-bit constant Rcon, and outputs data T.

Each of the key conversion units **60**˜**69** further includes the following elements: an exclusive-OR operation unit **604** that is connected to the exclusive-OR operation **603**, where the exclusive-OR operation unit **604** receives the first input data X**0** and the data T output from the exclusive-OR operation unit **603**, executes the exclusive-OR operation per bit between the first input data X**0** and the data T, and outputs the first output data Y**0**; and an exclusive-OR operation unit **605** which is connected to the exclusive-OR operation unit **604**, where the exclusive-OR operation unit **605** receives the second input data X**1** and the operation result of the exclusive-OR operation unit **604**, executes the exclusive-OR operation per bit between the second input data X**1** and the operation result, and outputs the second output data Y**1**.

Each of the key conversion units **60**˜**69** further includes: an exclusive-OR operation unit **606** which is connected to the exclusive-OR operation unit **605**, where the exclusive-OR operation unit **606** receives the third input data X**2** and the operation result of the exclusive-OR operation unit **605**, executes the exclusive-OR operation per bit between the third input data X**2** and the operation result, and outputs the third output data Y**2**; an exclusive-OR operation unit **607** which is connected to the exclusive-OR operation unit **606**, where the exclusive-OR operation unit **607** receives the fourth input data X**3** and the operation result of the exclusive-OR operation unit **606**, executes the exclusive-OR operation per bit between the fourth input data X**3** and the operation result, and outputs the fourth output data Y**3**; and a data concatenation unit **608** which is connected to the exclusive-OR operation units **604**˜**607**, where the data concatenation unit **608** concatenates the first˜fourth output data Y**0**˜Y**3**, and outputs the expansion key SK. Details of the process executed in each unit are described in the following explanations of the encryption process.

The following briefly describes the encryption process of the Rijndael encryption method executed by the encryption device **1300**. As indicated in **6** outputs the encryption key EK as the expansion key SK**0** to the key adding unit **500** within the data scrambling unit **5**. The key adding unit **500** executes the exclusive-OR operation per bit between the plain text PT and the expansion key SK**0** and outputs its result to the data conversion unit **50**. The data dividing unit **600** divides the encryption key EK by each 32 bits from its upper bit into four data blocks D**0**, D**1**, D**2** and D**3**.

Data entered into the data conversion unit **50** is sequentially processed for data conversion in each data conversion unit in the order from the data conversion unit **50** to the data conversion unit **58**, and a result finally processed in the final data conversion unit **59** is output as the ciphertext CT.

Each of the data conversion units **50**˜**58** executes the data conversion process based on the expansion keys SK**1**˜SK**9**. Also, the final data conversion unit **59** executes the data conversion process based on the expansion key SK**10**. Each of the expansion keys SK**1**˜SK**10** is generated in each of the key conversion units **60**˜**69** within the expansion key generating unit **6**, and respectively provided to the data conversion units **50**˜**58** and the final data conversion unit **59** in the data scrambling unit **5**. That is to say, there is a processing group at each stage, which consists of following processes (1) and (2) as a pair, and the data scrambling unit **5** executes 10 stages of them and generates the ciphertext CT.

Each of the key conversion units **60**˜**69** receives the first˜fourth input data X**0**˜X**3** (32 bits each), executes the key conversion process, and outputs the expansion key SK (128 bits) and the first˜fourth output data Y**0**˜Y**3**. The data rotation unit **601**, the data substituting unit **602** and the exclusive-OR operation unit **603** calculate the data T by conducting the operation expressed as the following formula (1) to the fourth input data X**3**.

*T=Rcon*(+)*Perm*(*ROTL*8(*X*3)) (1)

Here, ROTL**8** (X) indicates a result of the rotation bit shift by 8 bits executed to the data X in the upper bit direction (the left direction). Perm (X) indicates a result of a specific substituting process executed to the data X. An operator “(+)” indicates the exclusive-OR operation per bit. The constant Rcon is 32-bit fixed value data which is different in each key conversion units **60**˜**69**.

Each of the exclusive-OR operation units **604**˜**607** executes the operation indicated in the following formulas (2)˜(5) using the data T resulted from above, and finds the respective first˜fourth output data Y**0**˜Y**3**.

*Y*0=*T*(+)*X*0 (2)

*Y*1*=Y*0(+)*X*1 (3)

*Y*2*=Y*1(+)*X*2 (4)

*Y*3*=Y*2(+)*X*3 (5)

The data concatenation unit **608** gets the expansion key SK containing a relation expressed in the following formula (6). The operator “∥” indicates data concatenation. That is to say, the below formula (6) shows the 128-bit expansion key SK can be found by concatenating the first˜fourth output data Y**0**˜Y**3** having 32 bits each.

*SK=Y*0*∥Y*1*∥Y*2*∥Y*3 (6)

Each of the key conversion units **60**˜**69** outputs the expansion key SK and the first˜fourth output data Y**0**˜Y**3** obtained as a result of the above process.

**1400** includes the following elements: an expansion key inverse generating unit **8** that generates the expansion keys SK**10**˜SK**0** of 128 bits each in a reverse order of encryption, which is from the 128-bit encryption key EK; and a data inverse scrambling unit **7** that is connected to the expansion key inverse generating unit **8**, receives the expansion keys SK**10**˜SK**0** from the expansion key inverse generating unit **8**, executes a specific inverse data scrambling process to the 128-bit ciphertext using the expansion keys SK**10**˜SK**0**, and outputs the decryption text DT.

The expansion key inverse generating unit **8** includes the following elements: a data dividing unit **800** which receives the encryption key EK and divides it by each 32 bits from its upper level into four data blocks; a key conversion unit **80** which is connected to the data dividing unit **800**, where the key conversion unit **80** receives the four blocks, executes a specific operation to them and outputs four 32-bit data blocks; key conversion units **81**˜**88**, each of which is connected to the preceding key conversion unit, where each key conversion unit **81**˜**88** receives four 32-bit data blocks from the preceding key conversion unit, executes a specific operation to them, generates and outputs four 32-bit data blocks to the next key conversion unit; and a key conversion unit **89** which is connected to the key conversion unit **88**, where the key conversion unit **89** receives four 32-bit data blocks from the key conversion unit **88**, executes a specific operation to the four 32-bit data blocks, and generates and outputs the expansion key SK**10** and four 32-bit data blocks.

Since the specific operation executed by the key conversion units **80**˜**89** is the same as the specific operation executed by the key conversion units **60**˜**69** respectively, each of the key conversion units **80**˜**89** has the same structure as the key conversion unit indicated in

However, the key conversion units **80**˜**88** do not output the expansion keys SK**1**˜SK**9**, which are different from the key conversion units **60**˜**68**. Because of this, each of the key conversion units **80**˜**88** may have the structure of the key conversion unit shown in **608** is excluded.

The expansion key inverse generating unit **8** further includes the following elements: a key inverse conversion unit **90** which is connected to the key conversion unit **89**, where the key conversion unit **90** receives four 32-bit data blocks output from the key conversion unit **89**, executes a key inverse conversion process, which is explained later, generates and outputs the expansion key SK**9** and four 32-bit data blocks, and key inverse conversion units **91**˜**99**, each of which is connected to the key inverse conversion unit, where each of the inverse conversion units **91**˜**99** receives four 32-bit data blocks from the preceding key inverse conversion unit, executes the key inverse conversion process, which is explained later, generates and outputs the expansion key and four 32-bit data blocks.

Each of the expansion keys output from the key inverse conversion units **90**˜**99** are the respective expansion keys SK**9**˜SK**0**. The key inverse conversion unit **99** outputs four data blocks, but they are not used for other processes.

The data inverse scrambling unit **7** includes the following elements: a final data inverse conversion unit **70** which is connected to the key conversion unit **89**, where the final data inverse conversion unit **70** receives the expansion key SK**10** from the key conversion unit **89**, executes an inverse conversion process of the conversion process executed by the final data conversion unit **59** using the ciphertext CT and the expansion key SK**10**, and outputs the process result; and a data inverse conversion unit **71** which is connected to the final data inverse conversion unit **70** and the key inverse conversion unit **90**, where the data inverse conversion unit **71** respectively receives the process result and the expansion key SK**9** from the final data inverse conversion unit **70** and the key inverse conversion unit **90**, executes the inverse conversion process of the conversion process executed by the data conversion unit **58**, and outputs the process result.

The data inverse scrambling unit **7** further includes the following elements: data inverse conversion units **72**˜**79**, each of which is connected to the preceding data inverse conversion unit respectively and also connected the key inverse conversion units **91**˜**98** respectively, where each of the date inverse conversion units **72**˜**79** receives the expansion keys SK**8**˜SK**1** respectively from the key inverse conversion units **91**˜**98**, executes respectively the inverse conversion process of the conversion process executed by the data conversion units **57**˜**50**, and outputs the process result; and a key adding unit **700** which is connected to the data inverse conversion unit **79** and the key inverse conversion unit **99**, where the key adding unit **700** receives the process result and the expansion key SK**0** respectively from the data inverse conversion unit **79** and the key inverse conversion unit **99**, executes the inverse conversion process of the conversion process executed in the key adding unit **500**, and outputs the decryption text DT.

**90**˜**99**. Each of the key inverse conversion units **90**˜**99** executes the key inverse conversion process, which is equivalent to the inverse conversion of the key conversion process executed respectively in each of the key conversion units **60**˜**69** and **80**˜**89** based on the first˜fourth input data Y**0**˜Y**3**, which is 32 bits each, and outputs the first˜fourth output data Z**0**˜Z**3** and the 128-bit expansion key SK.

Each of the key inverse conversion units **90**˜**99** includes following units: an exclusive-OR operation unit **901** that executes the exclusive-OR operation per bit between the third input data Y**2** and the fourth input data Y**3**, and outputs the fourth output data Z**3**; an exclusive-OR operation unit **902** that executes the exclusive-OR operation per bit between the second input data Y**1** and the third input data Y**2**, and outputs the third output data Z**2**; and an exclusive-OR operation unit **903** that executes the exclusive-OR operation per bit between the first input data Y**0** and the second input data Y**1**, and outputs the second output data Z**1**.

Each of the key inverse conversion units **90**˜**99** further includes the following elements: a data rotation unit **905** which is connected to the exclusive-OR operation unit **901**, receives an output of the exclusive-OR operation unit **901**, where each of the key inverse conversion units **90**˜**94** executes the rotation bit shift by 8 bits to the output in the upper bit direction (the left direction), and outputs the result; and a data substituting unit **906** which is connected to the data rotation unit **905**, where the data rotation unit **905** receives the operation result from the data rotation unit **905**, executes a specific substituting process to the operation result, and outputs the result.

Each of the key inverse conversion units **90**˜**99** further includes the following elements: an exclusive-OR operation unit **907** that is connected to the data substituting unit **906**, where the exclusive-OR operation unit **907** receives the substituting result from the data substituting unit **906**, executes the exclusive-OR operation per bit between the substituting result and a 32-bit constant Rcon predefined in each of the key inverse conversion units **90**˜**99**, and outputs data T; an exclusive-OR operation unit **904** which is connected to the exclusive-OR operation unit **907**, where the exclusive-OR operation unit **904** receives the data T from the exclusive-OR operation unit **907**, executes the exclusive-OR operation per bit between the first input data Y**0** and the data T, and outputs the first output data Z**0**; and a data concatenation unit **908** which is connected to the exclusive-OR operation units **904**˜**901**, where the data concatenation unit **909** concatenates the first˜fourth output data Z**0**˜Z**3**, and outputs the expansion key SK. Details of the process taken in each unit are described in the following explanation of a decryption process.

The following briefly describes the decryption process of the Rijndael encryption method executed by the decryption device **1400**. As shown in **800** divides the 128-bit encryption key EK by each 32 bits from its upper bit into four 32-bit data blocks. A key conversion process is sequentially executed based on these four data blocks in the key conversion units **80**˜**89**. As mentioned above, the key conversion process executed in the key conversion units **80**˜**89** is the same as the key conversion process done in the key conversion units **60**˜**69** indicated in **1**˜SK**9** respectively generated in the key conversion units **80**˜**88** are not used for any subsequent processes.

A key conversion unit **89** outputs the generated expansion key SK to the final data inverse conversion unit **70** as the expansion key SK**10**. Subsequently, each of the key inverse conversion units **90**˜**99** generates the respective expansion keys SK**9**˜SK**0** in order. In parallel with the processes executed in the key conversion unit **89** and the key inverse conversion units **90**˜**99**, the final data inverse conversion unit **70**, the data inverse conversion units **71**˜**79** and key adding unit **700** execute a specific process respectively based on the expansion keys SK**10**˜SK**0**. The key adding unit **700** finally generates the decryption text DT, and outputs it.

Next, the following describes details of a process executed in the data inverse scrambling unit **7**. The process done in the data inverse scrambling unit **7** is equivalent to inverse conversion of the process taken place in the data scrambling unit **5** of the encryption device **1300** indicated in **70** executes the inverse conversion process of the process carried out by the final data conversion unit **59** with the expansion key SK**10**. Subsequently, the data inverse conversion units **71**˜**79** respectively conduct the inverse conversion process of the process in the data conversion units **58**˜**50** using the respective expansion keys SK**9**˜SK**1**. Lastly, the key adding unit **700** executes the inverse conversion process of the process executed in the key adding unit **500** using the expansion key SK**0** and generates the decryption text DT, and outputs it. As mentioned above, at the time of decryption, it is necessary to generate the expansion key in a reverse order of the encryption processes.

The following describes the key inverse conversion process executed in each of the key inverse conversion units **90**˜**99** indicated in

Each of the exclusive-OR operation units **901**˜**903** finds the respective second˜fourth output data Z**1**˜Z**3** by executing each operation shown in the following formulas (7)˜(**9**).

*Z*1*=Y*0(+)*Y*1 (7)

*Z*2*=Y*1(+)*Y*2 (8)

*Z*3*=Y*2(+)*Y*3 (9)

The data rotation unit **905**, the data substituting unit **906** and the exclusive-OR operation unit **907** calculate the data T by executing the operation indicated in the following formula (10) for the fourth output data Z**3**.

*T=Rcon*(+)*Perm*(*ROTL*8(*Z*3)) (10)

The exclusive-OR operation unit **904** finds the first output data Z**0**, which is the exclusive-OR operation per bit between the data T and the first input data Y**0** according to the next formula (11).

*Z*0*=T*(+)*Y*0 (11)

The data concatenation unit **908** concatenates the first˜fourth output data Z**0**˜Z**3** according to the next formula (12), and generates the 128-bit expansion key SK.

*SK=Z*0*∥Z*1*∥Z*2*∥Z*3 (12)

Each of the key inverse conversion units **90**˜**99** outputs the expansion key SK resulted from the above process and the first˜fourth output data Z**0**˜Z**3**.

As shown in **602** executes a non-linear process at the time of encryption according to this method. There is an impact on the expansion key SK and all of the output data from the data processed by the non-linear process via the exclusive-OR operation units **604**˜**607**. Therefore, though this method is a simple key conversion process, it can generate a highly random expansion key.

(Second Related Art)

The U.S. standard known as the Data Encryption Standard (DES) is the second related art. **10** used by an encryption device in the DES method. A key conversion unit **10** includes rotation shift units **101** and **102**, a data concatenation unit **103** which is connected to the rotation shift units **101** and **102**, and a data degenerating unit **104** which is connected to the data concatenation unit **103**.

The following describes actions of the key conversion unit **10**. The rotation shift unit **101** executes a rotation bit shift process by a specific number of bits to 28-bit first input data, and generates first rotation shift data. The rotation shift unit **102** executes the rotation bit shift process by a specific number of bits to 28-bit second input data, and generates second rotation shift data. The first rotation shift data and the second rotation shift data are output as first output data and second output data respectively from the key conversion unit **10**. On the other hand, the data concatenation unit **103** concatenates the first rotation shift data and the second rotation shift data to make 56-bit data, and outputs the data to the data degenerating unit **104**. The data degenerating unit **104** extracts data for 48 bits at a predefined bit location from the input data, and outputs the expansion key.

According to the encryption device in the DES method the same expansion key generation process can be applied to generate the expansion key both at the encryption process and at the decryption process because generating the expansion key is basically realized by a data shift process and a data extraction process. Accordingly, there is no difference between the encryption and the decryption processes regarding the processing workload necessary for generating the expansion key.

The above mentioned inventions as well as other related inventions contain deficiencies. In regards to the encryption method of the first related art, the time required to execute the generating process for the expansion key at the decryption stage is greater than the time required at the encryption stage. These timing differences occur for the following reasons. As shown in **5** of the encryption device **1300**, the encryption key EK is used as is in the key adding unit **500** that executes the first process. Therefore, a process of the data scrambling unit **5** can be executed in parallel with a process of the expansion key generating unit **6**.

On the other hand, as indicated in **7** of the decryption device **1400**, the final data inverse conversion unit **70**, which executes the process at first, must use the expansion key SK**10** provided from the expansion key inverse generating unit **8**. In order to get the expansion key SK**10**, a key conversion process needs to be carried out in the key conversion units **80**˜**89**. That is to say, the final data inverse conversion unit **70** can start its process only after the key conversion process is executed 10 times. Therefore, the decryption process takes more time than the time taken for the encryption process because these key conversion processes must take place.

When the above-described time gap is significantly large, the following problems arise. Consider, for example, a communication system where data is exchanged in a real time manner between a receiving device and a sending device. If the encryption device **1300** and the decryption device **1400** explained in the first related art are used in such a communication system, the sending device can encrypt data and send it in a real time manner. However, the receiving device cannot decrypt the encryption message in a real time manner because the decryption takes time. Accordingly, the prior art requires the use of a margin at the receiving device to temporarily store the encrypted data, which increases the cost of the receiving device.

Also, as shown in **1800** installed to a tollgate of expressways, data communication takes place between a tollgate antenna **1804** and an in-vehicle device **1802** which is attached to an automobile **1801** and authentication is executed between the tollgate antenna **1804** and the in-vehicle device **1802**. Because the automobile **1801** normally travels through the gate of the ETC system **1800** without stopping, a high-speed response is required for the ETC system **1800**. Therefore, if the conventional encryption device **1300** and decryption device **1400** are used in the ETC system **1800**, high-speed hardware will be required.

On the other hand, the problem of the first related art, being “the time required to generate the expansion key at the decryption takes longer than the time at the encryption”, is resolved in the second related art. However, the second related art still contains a problem where the expansion key is not sufficiently at random.

In the second related art, data is treated as an expansion key wherein a certain number of bits at a specific position are extracted from the concatenated data after a rotation bit shift is applied. Since a data combining process or a substituting process is not used for a process to generate the expansion key, the expansion key is not adequately random. Regarding the generation process of the expansion key in the second related art, the key cannot maintain a high security level. This is typically called a “weak key”. The weak key in the DES method is described, for example, in “Alfred J. Menezes, Paul C. van Oorschot, Scott A. Vanstone, “Handbook of Applied Cryptography”, CRC Press, 1997, pp. 256–pp. 259”.

In view of the above problems identified in the prior art, the present invention aims at providing an encryption system that reduces the time gap between encryption time and decryption time.

1. Additionally, the present invention also provides an encryption system that is capable of generating an expansion key with a high level of randomness and security. In order to achieve above objectives, this invention specifies an expansion key generating device which receives encryption key data as an input and it is operable to ouput plural expansion key data comprising: a data dividing unit operable to divide the encryption key data into plural part key data; and plural key conversion units, which are connected in series, operable to receive the plural part key data as input and output the plural expansion key data. Further, each of the plural key conversion units includes: an output calculation unit operable to receive the plural part key data or plural output data from a preceding key conversion unit as plural input data, execute a fixed conversion process to each of the plural input data in a way each bit value of each of the plural input data does not interfere each other, and output plural output data into a subsequent key conversion unit; and an expansion key calculation unit operable to combine the plural input data, and generate the expansion key data.

As mentioned above, because the output calculation unit can be separated from the expansion key calculation unit, and the process at the output calculation unit is a fixed conversion process for each of the input data such that each bit value of each input data does not interfere each other, it is possible to have a processing unit equivalent to what is resulted by executing processes at a specific number of stages in the output calculation unit. Therefore, once data is generated in the above equivalent processing unit at the time of decryption, it is possible to sequentially generate the expansion keys used for decrypting the ciphertext data by sequentially executing the inverse conversion processes of the processes executed by the key conversion unit. Accordingly, there is no need to execute the processes at a specific number of stages in the output calculation unit at the decryption, and thereby the time gap between the encryption and the decryption can be reduced.

Also, the expansion key calculation unit can provide a highly random and secure expansion key, because it combines plural part data when calculating the expansion key data.

For example, the output calculation unit executes a rotation shift operation by a specific number of bits to at least one of the plural input data, and the specific number of bits is not a measure of a number of bits of the input data, which the rotation shift operation is executed to.

Since the number of bits for the rotation shift operation is not made to a measure of the input data which the rotation shift rotation is executed to, it becomes hard to generate the same input data as the original input data even if the plural rotation shifts are executed to the input data. Therefore, a highly random and secure expansion key with a high level of security can be provided.

Also, the expansion key calculation unit executes a substituting process to at least one of the plural input data based on a specific substitution table in a halfway process of combining the plural input data.

The expansion key with a high level of randomness and security can be provided by inserting a non-linear process, such as the substituting process.

The present invention is not limited to an embodiment as such an expansion key generating device, but may also embody an encryption device equipped with such an expansion key generating device, and as a decryption device which decrypts a ciphertext data encrypted by an expansion key generating device. The present invention may also embody an encryption system comprised of an encryption device, a decryption device, and an expansion key generating method or a program having a computer function which operates as an expansion key generating device. Such a program may be widely distributed through a recording medium such as a Compact Disk-Read Only Memory (CD-ROM) or a transmission medium like the Internet.

These and the other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention. In the drawings:

**1100** as related to the embodiment of the present invention.

**11**˜**18** as related to the embodiment of the present invention.

**21**˜**27** as related to the embodiment of the present invention.

**28** as related to the embodiment of the present invention.

**1200** related to the embodiment of the present invention.

**31**˜**38** as related to the embodiment of the present invention.

**40** as related to the embodiment of the present invention.

**41**˜**47** as related to the embodiment of the present invention.

**160**.

**1500**.

**1520** and an exclusive-OR operation unit **1540** equivalent to it.

**1300** as related to the first related art.

**60**˜**69** as related to the first related art.

**1400** as related to the first related art.

**90**˜**99** as related to the first related art.

**10** as related to the second related art.

The following specifically describes an encryption system related to the present invention based on an embodiment with reference to drawings. The encryption system is comprised of an encryption device and a decryption device, which are explained later.

A data encryption unit **1100** includes the following elements: an expansion key generating unit **2** that generates eight expansion keys SK**0**˜SK**7** having 64 bits each based on a 128-bit encryption key EK; and a data scrambling unit **1** that is connected to the expansion key generating unit **2**, receives the expansion keys SK**0**˜SK**7** from the expansion key generating unit **2**, executes a data scramble by repeating a specific data conversion process to a plain text PT by using the expansion keys SK**0**˜SK**7**, and generates a 64-bit ciphertext CT.

The data scrambling unit **1** consists of eight data conversion units **11**˜**18** that are concatenated vertically. The expansion key generating unit **2** is made up of a data dividing unit **20**, seven key conversion units **21**˜**27** and a final key conversion unit **28**, which are concatenated vertically.

**11**˜**18**. Each of the data conversion units **11**˜**18** includes the following elements: an exclusive-OR operation unit **111** that is connected to either one of the key conversion units **21**˜**27** or the final key conversion unit **28**, receives the expansion key SK (one of SK**0**˜SK**7**) from one of the key conversion units, executes the exclusive-OR operation per bit between the expansion key SK and input data X, and outputs data A; and a data dividing unit **112** that is connected to the exclusive-OR operation unit **111**, receives the data A from the exclusive-OR operation unit **111**, and divides the data A into four data blocks B**0**˜B**3**.

Each of the data conversion units **11**˜**18** further includes the following elements: data substituting units **113**˜**116** that are connected to the data dividing unit **112**, receive the respective data blocks B**0**˜B**3** from the data dividing unit **112**, and substitute the respective data blocks C**0**˜C**3** for the respective data blocks B**0**˜B**3** in a method explained later; and a data concatenation unit **117** that is connected to the data substituting units **113**˜**116**, receives the data blocks C**0**˜C**3** respectively from the data substituting units **113**˜**116**, concatenates the data blocks C**0**˜C**3** in a method, which is explained later, and outputs data Y.

**21**˜**27**. Each of the key conversion units **21**˜**27** includes the following elements: an expansion key calculation unit **210** that receives first˜fourth input data X**0**˜X**3** having 32 bits each from the data dividing unit **20** or the preceding key conversion unit, and calculates a 64-bit expansion key SK from the first˜fourth input data X**0**˜X**3**; and an output calculation unit **230** that calculates the first˜fourth output data Y**0**˜Y**3**, which are used as input for a subsequent key conversion unit or the final key conversion unit **28**, from the first˜fourth input data X**0**˜X**3**.

The expansion key calculation unit **210** includes the following elements: an exclusive-OR operation unit **211** that executes the exclusive-OR operation per bit between the second input data X**1** and the fourth input data X**3** and calculates 32-bit data A; a data substituting unit **212** that is connected to the exclusive-OR operation unit **211**, receives the data A from the exclusive-OR operation unit **211** and substitutes the data B for the data A in a method explained later; and an exclusive-OR operation unit **213** that is connected to the data substituting unit **212**, receives the data B from the data substituting unit **212**, executes the exclusive-OR operation per bit between the data B and the third input data X**2**, and calculates data C.

The expansion key calculation unit **210** further includes the following elements: an exclusive-OR operation unit **214** that is connected to the exclusive-OR operation unit **213**, which receives the data C from the exclusive-OR operation unit **213**, executes the exclusive-OR operation per bit between the data C and the second input data X**1**, and calculates data D; an exclusive-OR operation unit **215** that is connected to the exclusive-OR operation unit **214**, which receives the data D from the exclusive-OR operation **214**, executes the exclusive-OR operation per bit between the data D and the first input data X**0** and calculates data E; and a data concatenation unit **216** that is connected to the exclusive-OR operation units **213** and **215**, which receives the data C and the data E respectively from the exclusive-OR operation units **213** and **215**, concatenates the data C and the data E, and outputs it as a 64-bit expansion key SK.

An output calculation unit **230** includes the following elements: a data rotation unit **217** that executes a rotation bit shift by 1 bit to the first input data X**0** in a lower bit direction (a right direction), and outputs it as the fourth output data Y**3**; a data rotation unit **218** that executes a rotation bit shift by 5 bits to the second input data X**1** in the lower bit direction (the right direction), and outputs it as the first output data Y**0**; a data rotation unit **219** that executes a rotation bit shift by 9 bits to the third input data X**2** in the lower bit direction (the right direction), and outputs it as the second output data Y**1**; and a data rotation unit **220** that executes a rotation bit shift by 13 bits to the fourth input data X**3** in the lower bit direction (the right direction), and outputs it as the third output data Y**2**.

**28**. The final key conversion unit **28** has a configuration of the key conversion unit in **230** is excluded. The final key conversion unit **28** includes the expansion key calculation unit **280**.

The expansion key calculation unit **280** includes the following elements: an exclusive-OR operation unit **281**; a data substituting unit **282** connected to the exclusive-OR operation unit **281**; an exclusive-OR operation unit **283** connected to the data substituting unit **282**; an exclusive-OR operation unit **284** connected to the exclusive-OR operation unit **283**; an exclusive-OR operation unit **285** connected to the exclusive-OR operation unit **284**: and a data concatenation unit **286** connected to the exclusive-OR operation units **283** and **285**.

The structures of the exclusive-OR operation units **281**, **283**˜**285**, the data substituting unit **282** and the data concatenation unit **286** are the same as the respective structures of the exclusive-OR operation units **211**, **213**˜**215**, the data substituting unit **212** and the data concatenation unit **216** of the expansion key calculation unit **210** in

The following describes actions taken by the encryption device **1100** with reference to **5**.

The following explanation is for an overall process flow of the encryption device shown in

A data dividing unit **20** in the expansion key generating unit **2** divides a 128-bit encryption key EK by each 32 bits from its upper level into four data blocks, and outputs them to the key conversion unit **21**. The key conversion unit **21** executes the key conversion process, which is explained later, for the input four blocks, and calculates a 64-bit expansion key SK**0** and four 32-bit data blocks. The key conversion unit **21** outputs the expansion key SK**0** to the data conversion unit **11** and outputs the calculated four data blocks to a subsequent key conversion unit **22**.

The data conversion unit **11** executes the data conversion process, which is explained later, on a 64-bit plain text PT based on the input expansion key SK**0**, and calculates 64 bit data. The data conversion unit **11** outputs the calculated data to a subsequent data conversion unit **12**.

The key conversion unit **22** executes the same key conversion process as the key conversion unit **21** to the four 32-bit data blocks input from the preceding key conversion unit **21**, and calculates the expansion key SK**1** and the four 32-bit data blocks. The key conversion unit **22** outputs the expansion key SK**1** to the data conversion unit **12**, and outputs the calculated four data blocks to a subsequent key conversion unit **23**.

The data conversion unit **12** executes the same data conversion process as the data conversion unit **11** to the data input from the preceding data conversion unit **11** based on the input expansion key SK**1**, and calculates 64-bit data. The data conversion unit **12** outputs the calculated data to a subsequent data conversion unit **13**.

The same processes are executed in the key conversion units **23**˜**27** and the data conversion units **13**˜**17**. The final key conversion unit **28** executes the final key conversion process, which is explained later, to the four data blocks input from the key conversion unit **27**, finds the expansion key SK**7**, and outputs it to the data conversion unit **18**.

The data conversion unit **18** executes the same data conversion process as the data conversion unit **11** for the data input from the data conversion unit **17** based on the expansion key SK**7**, calculates 64-bit ciphertext CT, and outputs it.

The following describes a data conversion process executed by each of the data conversion units **1**˜**18** in **1**˜**18** executes the data conversion process to the 64-bit input data X based on the 64-bit expansion key SK, and outputs 64-bit output data Y. The input data X is either the plain text PT or the data output from the preceding data conversion unit. The expansion key SK is one of SK**0**˜SK**7** respectively output from the key conversion units **21**˜**28**.

The exclusive-OR operation unit **111** executes the exclusive-OR operation per bit between the input data X and the expansion key SK, as shown in the following formula (13), and finds the 64-bit data A.

*A=X*(+)*SK* (13)

The data dividing unit **112** receives the data A from the exclusive-OR operation **111**, and divides the data A into four data blocks B**0**, B**1**, B**2** and B**3** from its first four bits on the top. That is to say, a relationship indicated in the following formula (14) is established between the data A and the data blocks B**0**˜B**3**.

*A=B*0*∥B*1*∥B*2*∥B*3 (14)

The data dividing unit **112** outputs four data blocks B**0**˜B**3** one by one to the data substituting units **113**˜**116**.

According to the following formula (15), the data substituting unit **113** finds 16-bit data C**0** based on the 16-bit data B**0** input from the data dividing unit **112**.

*C*0*=S*box[*B*0*h]∥S*box*[B*0*l]* (15)

Sbox here indicates a substitution table. As shown in **0** *h *indicates 8 bits in an upper level of the data B**0**, whereas B**0** *l *indicates 8 bits in a lower level of the data B**0**.

That is to say, Sbox [B**0** *h*] shows the B**0** *h*-th element in the substitution table Sbox, while Sbox [B**0** *l*] shows the B**0** *l*-th element in the substitution table Sbox. Data C**0** is data generated by concatenating these two elements.

The substitution table Sbox used here is the one described in “S-box design considering the security against known attacks on block ciphers”, Technical Report of IEICE, Vol. 98 No. 48, ISEC98-13, (in Japanese), (July, 1998) written by Shiho Moriai, Kazumaro Aoki, Masayuki Kanda, Youichi Takashima, and Kazuo Ohta. However, the substitution table Sbox is not limited to this, and may be something else.

The data substituting units **114**˜**116** receive the respective data blocks B**1**˜B**3** from the data dividing unit **112**, find the data blocks C**1**˜C**3** respectively, and output them. As a process executed in each of the data substituting units **114**˜**116** is the same as the process executed by the data substituting unit **113**, its detailed explanation is not repeated here.

A data concatenation unit **117** receives the data blocks C**0**˜C**3** respectively from the data substituting units **113**˜**116**, concatenates the data blocks C**0**˜C**3** according to the following formula (16), finds 64-bit data Y, and outputs it.

*Y=C*0*∥C*1*∥C*2*∥C*3 (16)

The following describes the key conversion process executed in each of the key conversion units **21**˜**27** shown in **21**˜**27** executes the expansion key calculation process and the output calculation process, which are explained later, to the first˜fourth input data X**0**˜X**3**, calculates the expansion key SK and the first˜fourth output data Y**0**˜Y**3**, and outputs them. The first˜fourth input data X**0**˜X**3** are four 32-bit data blocks output from the data dividing unit **20** or the preceding key conversion unit. The expansion key SK is one of SK**0**˜SK**6** respectively input to the data conversion units **11**˜**17**.

The following explains the expansion key calculation process executed in the expansion key calculation unit **210**.

The exclusive-OR operation unit **211** executes the exclusive-OR operation per bit between the second input data X**1** and the fourth input data X**3** according to the following formula (17), and finds 32-bit data A.

*A=X*1(+)*X*3 (17)

A data substituting unit **212** receives the data A from the exclusive-OR operation unit **211**, and finds 32-bit data B indicated according to the following formula (18) using the same substitution table Sbox as the substitution table used in the data conversion units **11**˜**18**.

*B=S*box[*A*0*]∥S*box[*A*1*]∥S*box[*A*2*]∥S*box[*A*3] (18)

Data values, which are obtained by dividing the data A by each 8 bits from its upper level, are respectively treated as A**0**, A**1**, A**2** and A**3**.

The exclusive-OR operation unit **213** receives the data B from the data substituting unit **212**, executes the exclusive-OR operation per bit between the data B and the third input data X**2** according to the following formula (19), and gets 32-bit data C.

*C=B*(+)*X*2 (19)

The exclusive-OR operation unit **214** receives the data C from the exclusive-OR operation unit **213**, and executes the exclusive-OR operation per bit between the data C and the second input data X**1** according to the following formula (20), and gets 32-bit data D.

*D=C*(+)*X*1 (20)

The exclusive-OR operation unit **215** receives the data D from the exclusive-OR operation unit **214**, and executes the exclusive-OR operation per bit between the data D and the first input data X**0** according to the following formula (21), and gets 32-bit data E.

*E=D*(+)*X*0 (21)

The data concatenation unit **216** receives the data C and E respectively from the exclusive-OR operation units **213** and **215**, concatenates the data C and E according to the following formula (22), and outputs it as a 64-bit expansion key SK.

*SK=C∥E* (22)

The following describes a process (an output calculation process) to calculate the first˜fourth output data Y**0**˜Y**3** in the output calculation unit **230**.

The data rotation units **217**˜**220** calculate the fourth output data Y**3**, the first output data Y**0**, the second output data Y**1** and the third output data Y**2** respectively according to the following formulas (23)˜(26).

*Y*3*=ROTR*1(*X*0) (23)

*Y*0*=ROTR*5(*X*1) (24)

*Y*1*=ROTR*9(*X*2) (25)

*Y*2*=ROTR*13(*X*3) (26)

ROTR**1** (X), ROTR**5** (X), ROTR**9** (X) and ROTR**13** (X) respectively indicate results of the data X where the respective rotation bit shift by 1 bit, 5 bits, 9 bits and 13 bits is applied to in a lower side direction (a right direction).

The following describes the final key conversion process executed by the final key conversion unit **28** in **280** of the final key conversion unit **28** calculates the expansion key SK**7** by taking the same actions as the expansion key calculation unit **210** in

The data decryption device **1200** includes the following elements: an expansion key inverse generating unit **4** that generates eight expansion keys SK**7**˜SK**0** of 64 bits each in a reverse order of the encryption based on the 128-bit encryption key EK; and a data inverse scrambling unit **3** that is connected to the expansion key inverse generating unit **4**, receives the expansion keys SK**7**˜SK**0** from the expansion key inverse generating unit **4**, and generates the decryption text DT by repeating the inverse data conversion process, which is explained later, to the ciphertext CT using the expansion keys SK**7**˜SK**0**.

The data inverse scrambling unit **3** consists of eight data inverse conversion units **31**˜**38** concatenated vertically. The expansion key inverse generating unit **4** is made up of the key modification unit **40**, seven key inverse conversion units **41**˜**47** and a final key conversion unit **48** concatenated vertically.

**31**˜**38**. Each of the data inverse conversion units **31**˜**38** includes a data dividing unit **311** that receives 64-bit input data Y (the ciphertext CT or the output data of the preceding data inverse conversion unit) and divides the data Y into four data blocks A**0**˜A**3**, and data inverse substituting units **312**˜**315** that are connected to the data dividing unit **311**, receive the respective data blocks A**0**˜A**3** from the data dividing unit **311** and substitute the respective data blocks B**0**˜B**3** for the respective data blocks A**0**˜A**3** in a method, which is explained later.

Each of the data inverse conversion units **31**˜**38** further includes the following elements: a data concatenation unit **316** that is connected to the data inverse substituting units **312**˜**315**, receives the data blocks B**0**˜B**3** from the data inverse substituting units **312**˜**315**, concatenates the data blocks B**0**˜B**3**, and outputs it; the exclusive-OR operation unit **317** that is connected to the data concatenation unit **316**, receives the concatenated result output from the data concatenation unit **316**, executes the exclusive-OR operation per bit between the concatenated result and the expansion key SK, and outputs data Z.

**40**. The key modification unit **40** receives the first˜fourth input data I**0**˜I**3** of 32 bits each, executes a process, which is explained later, and calculates the first˜fourth output data J**0**˜J**3**. The key modification unit **40** includes the following elements: a data rotation unit **401** that executes the rotation bit shift by 51 bits to the first input data I**0** in the lower bit direction (the right direction), and outputs it as the second output J**1**; a data rotation unit **402** that executes the rotation bit shift by 47 bits to the second input data I**1** in the lower bit direction (the right direction), and outputs it as the third output data J**2**; a data rotation unit **403** that executes the rotation bit shift by 43 bits to the third input data I**2** in the lower level bit direction (the right direction), and outputs it as the fourth output data J**3**; a data rotation unit **404** that executes the rotation bit shift by 55 bits to the fourth input data I**3** in the lower level bit direction (the right direction), and outputs it as the first output data J**0**.

**41**˜**47**. Each of the key inverse conversion units **41**˜**47** includes the following elements: an expansion key calculation unit **410** that receives the first˜fourth input data Y**0**˜Y**3** having 32 bits each from the key modification unit **40** or the preceding key inverse conversion unit, and calculates 64-bit expansion key SK from the first˜fourth input data Y**0**˜Y**3**; and an output inverse calculation unit **430** that calculates the first˜fourth output data Z**0**˜Z**3** which is an input to the subsequent key inverse conversion unit or the final key conversion unit **48** from the first˜fourth input data Y**0**˜Y**3**.

The expansion key calculation unit **410** includes the following elements: an exclusive-OR operation unit **411** that executes the exclusive-OR operation per bit between the second input data Y**1** and the fourth input data Y**3**, and calculates 32-bit data A; a data substituting unit **412** that is connected to the exclusive-OR operation unit **411**, receives the data A from the exclusive-OR operation unit **411**, and substitutes the data B for the data A in a method, which is explained later; an exclusive-OR operation unit **413** that is connected to the data substituting unit **412**, receives the data B from the data substituting unit **412**, executes the exclusive-OR operation per bit between the data B and the third input data Y**2**, and calculates data C.

The expansion key calculation unit **410** further includes the following elements: an exclusive-OR operation unit **414** that is connected to the exclusive-OR operation unit **413**, receives the data C from the exclusive-OR operation unit **413**, executes the exclusive-OR operation per bit between the data C and the second input data Y**1**, and calculates data D; an exclusive-OR operation unit **415** that is connected to the exclusive-OR operation unit **414**, receives the data D from the exclusive-OR operation unit **414**, executes the exclusive-OR operation per bit between the data D and the first input data Y**0**, and calculates data E; and a data concatenation unit **416** that is connected to the exclusive-OR operation units **413** and **415**, receives the data C and the data E respectively from the exclusive-OR operation units **413** and **415**, concatenates the data C and the data E, and outputs it as a 64-bit expansion key SK.

The output inverse calculation unit **430** includes the following elements: a data rotation unit **417** that executes the rotation bit shift by 5 bits to the first input data Y**0** in the upper level direction (the left direction), and outputs it as the second output data Z**1**; a data rotation unit **418** that executes the rotation bit shift by 9 bits to the second input data Y**1** in the upper level direction (the left direction), and outputs it as the third output data Z**2**; a data rotation unit **419** that executes the rotation bit shift by 13 bits to the third input data Y**2** in the upper direction (the left direction), and outputs it as the fourth output data Z**3**; and a data rotation unit **420** that executes the rotation bit shift by 1 bit to the fourth input data Y**3** in the upper direction (the left direction), and outputs it as the first output data Z**0**.

The final key conversion unit **48** indicated in **28** in

The following describes actions taken by the decryption device **1200** with reference to **12**.

An overall process flow of the decryption device **1200** shown in

The key modification unit **40** within the expansion key inverse generating unit **4** executes, after internally dividing a 128-bit encryption key EK into four 32-bit data blocks, the key modification process, which is explained later, and calculates four 32-bit data blocks. The key modification unit **40** outputs the calculated four data blocks to the key inverse conversion unit **41**.

The key inverse conversion unit **41** executes the key inverse conversion process, which is explained later, based on the input four data blocks, and calculates a 64-bit expansion key SK**7** and four 32-bit data blocks. The key inverse conversion unit **41** outputs the expansion key SK**7** to the data inverse conversion unit **31**, and outputs the four data blocks to the next key inverse conversion unit **42**.

The data inverse conversion unit **31** executes the inverse data conversion process, which is explained later, to a 64-bit ciphertext CT based on the input expansion key SK**7**, calculates 64-bit data, and outputs it to the next data inverse conversion unit **32**.

The key inverse conversion unit **42** executes the same process as the key inverse conversion unit **41** based on the four data blocks input from the preceding key inverse conversion unit **41**, and calculates the expansion key SK**6** and four data blocks. The key inverse conversion unit **42** outputs the expansion key SK**6** to the data inverse conversion unit **32**, and outputs the calculated four data blocks to the key inverse conversion unit **43**.

The data inverse conversion unit **32** executes the same inverse data conversion process as the data inverse conversion unit **31** to the data input from the preceding data inverse conversion unit **31** based on the expansion key SK**6**, calculates 64-bit data, and outputs it to the subsequent data inverse conversion unit **33**.

The same operation is executed in the key inverse conversion units **43**˜**47** and the data inverse conversion units **33**˜**37**. The final key conversion unit **48** executes the same process as the final key conversion process used in the final key conversion unit **28** in **47**, calculates the expansion key SK**0**, and outputs it to the data inverse conversion unit **38**.

The data inverse conversion unit **38** executes the same inverse data conversion process as the data inverse conversion unit **31** to the data input from the data inverse conversion unit **37** based on the expansion key SK**0**, calculates and outputs a 64-bit decryption text DT.

The following describes the inverse data conversion process executed in each of the data inverse conversion units **31**˜**38** indicated in

The data dividing unit **311** divides the 64-bit data Y (the ciphertext CT or the data Z output from the preceding data inverse conversion unit) by each 16 bits from its upper level into four data blocks A**0**, A**1**, A**2** and A**3**. That is to say, the relationship indicated in the following formula (27) is established between the data Y and the data blocks A**0**˜A**3**.

*Y=A*0*∥A*1*∥A*2*∥A*3 (27)

The data dividing unit **311** outputs the data blocks A**0**˜A**3** to the data inverse substituting units **312**˜**315** respectively.

The data inverse substituting unit **312** finds 16-bit data block B**0** according to the following formula (28) based on the 16-bit data A**0** input from the data dividing unit **311**.

*B*0*=InvS*box[*A*0*h]∥InvS*box[*A*01] (28)

InvSbox here indicates an inverse substitution table that executes an inverse substitution of the substitution table Sbox explained above. The inverse substitution table consists of arrays having 256 elements as shown in **0** *h *indicates the first 8 bits of the data block A**0**, whereas A**0** *l *shows the last 8 bits of the data block A**0**.

That is to say, InvSbox [A**0** *h*] shows the A**0** *h*-th element in the inverse substitution table InvSbox, while InvSbox [A**0** *l*] indicates the A**0** *l*-th element in the inverse substitution table InvSbox. The data block B**0** is the data generated by concatenating these two elements.

The inverse substitution table InvSbox used here is the one created based on the substitution table Sbox used by the data substituting units **113**˜**116** in

In short, the relationship indicated in the following formula (29) is established between the substitution table Sbox and the inverse substitution table InvSbox.

*InvS*box[*S*box[*I]]=i*(*i=*0˜255) (29)

Each of the data inverse substituting units **313**˜**315** receives the respective data blocks A**1**˜A**3** from the data dividing unit **311**, and gets the data blocks B**1**˜B**3** respectively, and outputs them. Since the process executed by each of the data inverse substituting units **313**˜**315** is the same as the process done in the data inverse substituting unit **312**, its detailed explanation is not repeated here.

The data concatenation unit **316** respectively receives the data blocks B**0**˜B**3** from the data inverse substituting units **312**˜**315**, concatenates the data blocks B**0**˜B**3** according to the following formula (30), gets the 64-bit data Z, and outputs it.

*Z=B*0*∥B*1*∥B*2*∥B*3 (30)

The following describes the key modification process executed by the key modification unit **40** in **40** executes the process with an input of the 128-bit encryption key EK, and makes each 32 bits from its upper side of the encryption key EK be the first˜fourth input data I**0**˜I**3**.

Each of the data rotation units **401**˜**404** calculates the second output data J**1**, the third output data J**2**, the fourth output data J**3** and the first output data J**0** respectively according to following formulas (31)˜(34).

*J*1*=ROTR*51 (*I*0) (31)

*J*2*=ROTR*47(*I*1) (32)

*J*3*=ROTR*43(*I*2) (33)

*J*0*=ROTR*55(*I*3) (34)

ROTR**51** (I), ROTR**47** (I), ROTR**43** (I), and ROTR**55** (I) here show results of the rotation bit shift that shifts the data I by 51 bits, 47 bits, 43 bits and 55 bits each in the lower direction (the right direction).

Finally, the key modification unit **40** outputs the first˜fourth output data J**0**˜J**3**.

The following describes a meaning of a shift volume in the data rotation unit **401** of the key modification unit **40**. The data rotation process is executed in the output calculation unit **230** in **0**˜X**3** input to the key conversion unit **21**, and ROTR**5** (X**1**), ROTR**9** (X**2**), ROTR**13** (X**3**) and ROTR**1** (X**0**) are obtained as the first˜fourth output data Y**0**˜Y**3** respectively as indicated in Table 1.

If the first˜fourth output data Y**0**˜Y**3** obtained in the key conversion unit **21** are supposed to be the first˜fourth input data X**0**˜X**3** respectively in the key conversion unit **22**, the same data rotation process is executed, and ROTR**14** (X**2**), ROTR**22** (X**3**), ROTR**14** (X**0**) and ROTR**6** (X**1**) are obtained as the first˜fourth output data Y**0**˜Y**3** in the key conversion unit **22**, which are as shown in Table 1.

If the same process is executed to the key conversion units **23**˜**27**, the result shown in Table 1 can be obtained. Therefore, if the key modification unit **40** having the structure shown in **21**˜**27** can be obtained.

TABLE 1 | ||||

OUTPUT | ||||

KEY | FIRST OUTPUT | SECOND OUPTUT | THIRD OUTPUT | FOURTH OUTPUT |

CONVERSION UNIT | DATA Y0 | DATA Y1 | DATA Y2 | DATA Y3 |

KEY | ROTR5(X1) | ROTR9(X2) | ROTR13(X3) | ROTR1(X0) |

CONVERSION UNIT 21 | ||||

KEY | ROTR14(X2) | ROTR22(X3) | ROTR14(X0) | ROTR6(X1) |

CONVERSION UNIT 22 | ||||

KEY | ROTR27(X3) | ROTR23(X0) | ROTR19(X1) | ROTR15(X2) |

CONVERSION UNIT 23 | ||||

KEY | ROTR28(X0) | ROTR28(X1) | ROTR28(X2) | ROTR28(X3) |

CONVERSION UNIT 24 | ||||

KEY | ROTR33(X1) | ROTR37(X2) | ROTR41(X3) | ROTR29(X0) |

CONVERSION UNIT 25 | ||||

KEY | ROTR42(X2) | ROTR50(X3) | ROTR42(X0) | ROTR34(X1) |

CONVERSION UNIT 26 | ||||

KEY | ROTR55(X3) | ROTR51(X0) | ROTR47(X1) | ROTR43(X2) |

CONVERSION UNIT 27 | ||||

Although **40** having 7 stages of the key conversion units, it is possible to have a key modification unit regardless of a number of stages of the key conversion units. For example, when there are 6 stages of the key conversion units, the key modification unit **160** in **40**. The key modification unit **160** is created based on Table 1. Each of the data rotation units **1601**˜**1604** of the key modification unit **160** executes a rotation bit shift process by 42 bits, 34 bits, 42 bits and 50 bits respectively to the input data in a lower bit direction (a right direction). However, the rotation bit shift by 32 bits is equal to the rotation bit shift by 0 bit (i.e. no process takes place). Therefore, it is possible to reduce the number of the rotation bit shifts by setting the number of the rotation bit shifts to 10 bits, 2 bits, 10 bits and 18 bits respectively in the data rotation units **1601**˜**1604**.

Also, the number of the rotation bit shifts in the data rotation units **401**˜**404** of the key modification unit **40** shown in

The following describes the key inverse conversion process executed by the key inverse conversion units **41**˜**47** shown in **41**˜**47** executes the expansion key calculation process and the data conversion process, which are explained later, to the first˜fourth input data Y**0**˜Y**3**, calculates the expansion key SK and the first˜fourth output data Z**0**˜Z**3**, and outputs them. The first˜fourth input data Y**0**˜Y**3** are the four 32-bit data blocks output from the key modification unit **40** or the preceding inverse conversion unit. The expansion key SK is one of SK**7**˜SK**1** input to the respective data inverse conversion units **31**˜**37**.

The following describes the expansion key calculation process executed in the expansion key calculation unit **410**.

The exclusive-OR operation unit **411** executes an exclusive-OR operation per bit between the second input data Y**1** and the fourth input data Y**3** according to the following formula (35), and gets 32-bit data A.

*A=Y*1(+)*Y*3 (35)

The data substituting unit **412** receives data A from the exclusive-OR operation unit **411**, and gets 32-bit data B, which is in a relationship indicated in the following formula (36), using the same substitution table Sbox as the substitution table used in the data conversion units **11**˜**18** at the time of encryption.

*B=S*box[*A*0*]∥S*box[*A*1*]∥S*box[*A*2*]∥S*box[*A*3] (36)

The data is divided by each 8 bits from its upper level of the data A is supposed to be A**0**, A**1**, A**2** and A**3** each.

The exclusive-OR operation unit **413** receives the data B from the data substituting unit **412**, executes the exclusive-OR operation per bit between the data B and the third input data Y**2** according to the following formula (37), and gets 32-bit data C.

*C=B*(+)*Y*2 (37)

The exclusive-OR operation unit **414** receives the data C from the exclusive-OR operation unit **413**, executes the exclusive-OR operation per bit between the data C and the second input data Y**1** according to the following formula (38), and gets 32-bit data D.

*D=C*(+)*Y*1 (38)

The exclusive-OR operation unit **415** receives the data D from the exclusive-OR operation unit **414**, executes the exclusive-OR operation per bit between the data D and the first input data Y**0** according to the following formula (39), and gets 32-bit data E.

*E=D*(+)*Y*0 (39)

The data concatenation unit **416** receives the data C and the data E respectively from the exclusive-OR operation units **413** and **415**, concatenates the data C and the data E according to the following formula (40), and outputs it as 64 bit expansion key SK.

*SK=C∥E* (40)

The following describes a process (a data conversion process) that calculates the first˜fourth output data Z**0**˜Z**3** in the output inverse calculation unit **430**.

The data rotation units **417**˜**420** calculate the second output data Z**1**, the third output data Z**2**, the fourth output data Z**3** and the first output data Z**0** respectively according to the following formulas (41)˜(44).

*Z*1*=ROTL*5(*Y*0) (41)

*Z*2*=ROTL*9(*Y*1) (42)

*Z*3*=ROTL*13(*Y*2) (43)

*Z*0*=ROTL*1(*Y*3) (44)

ROTL**5** (Y), ROTL**9** (Y), ROTL**13** (Y) and ROTL**1** (Y) here show results of the rotation bit shift by 5 bits, 9 bits, 13 bits and 1 bit each executed to the data Y in the upper bit direction (the left direction).

The following describes an effect of the encryption system in the embodiment explained above in comparison with conventional technologies.

As shown in **10** used in the final data inverse conversion unit **70** within the decryption device **1400**. Because of this, the decryption process in the first related art requires a large amount of processing time when compared to the time taken for the encryption process.

However, as shown in **40** in the decryption device **1200** related to the present embodiment. This is equivalent to repeating the process in the output calculation unit **230** of the key conversion unit, shown in **230** 7 times is equivalent to executing the data rotation process 4 times, as shown in the key modification unit **40**. A comparison of the overhead processing volume between the both cases is as follows.

In the first related art, to execute the process of the key conversion unit one time requires 5 times of the exclusive-OR operation, once of the substituting process and once of the data rotation process. Therefore, if this is executed 9 times, 45 times of the exclusive-OR operation, 9 times of the substitution process and 9 times of the data rotation process are required as the overhead. On the other hand, in the decryption device **1200** as related to the present embodiment, the process necessary as the overhead is 4 times of the data rotation process only.

That is to say, the overheads of the present invention are much less than the ones of the first related art. This is realized by separating the expansion key calculation unit **210**, which calculates the expansion key, from the output calculation unit **230**, which serves as input to the subsequent key conversion unit, in the key conversion unit indicated in **230** only with the data rotation process.

Also, since the data rotation process can be realized by arranging a distribution pattern of signal lines when it is installed in hardware, it does not cause data delay. Because of this, when the decryption device **1200** shown in **1200** is realized in software, the rotation bit shift can be executed at high speed in most of processors. Therefore, it is possible to say that the overhead is so small that it can be ignored.

Next, the randomness of the expansion key generated in the system is examined. At the time of encryption, the output of the data substituting unit **212** in the key conversion units **21**˜**27** shown in **213**˜**215**. That is to say, the non-linear process by using the substitution table of the data substituting unit **212** has an impact on an entire range of the expansion keys through the data combining process by the exclusive-OR operation units **213**˜**215**. It means to perform the same effect as the key conversion units **60**˜**69** in the first related art. Also, all of the first˜fourth input data X**0**˜X**3** are used as the input data in the data combining process executed by the exclusive-OR operation units **211** and **213**˜**215**. Therefore, even when only a bit of the encryption key EK is changed, it is possible to say that all of the expansion keys SK**0**˜SK**7** generated by it are changed. From the above, it is possible to say that the generated expansion key contains sufficient randomness.

Furthermore, each of the data rotation units **217**˜**220** within the output calculation unit **230** uses 1, 5, 9 and 13 bits respectively as a number of times for its data rotation. These numbers of bit(s) are not a measure of the number of bits (32 bits) respectively input to the data rotation unit **217**. Compared to this, in the second related art, the number of bits, i.e. 8 that is a measure of **32**, is used as the number of bits for the data rotation in the bit rotation unit **601** indicated in **230** within the key conversion units **21**˜**27** in the present embodiment, a high data scrambling performance is realized even in the output calculation unit **230**.

The data rotation process is executed to all of the 32-bit data blocks in the output calculation unit **230**, but it is not limited to this structure. As long as the data rotation process is executed to at least one of the four data blocks, it is sufficient. Also, the number of data rotations is not limited to the values indicated in the present embodiment. As long as it is not a measure of the data block size, it may be other number of rotations.

Besides, rather than the data rotation process, the output calculation unit **230** may conduct a fixed conversion process to the first˜fourth input data X**0**˜X**3** in a way each bit value of each of the input data does not interfere each other. For example, a bit replacing unit **1500** indicated in **217**. The bit replacing unit **1500** receives the first input data X**0** having 32 bits, replaces the bit positions to prevent each bit value from being interfered by the other, and outputs it as the fourth output data Y**3**.

Because each bit value does not interfere each other with such a conversion, it is possible to create the key modification unit such as the one indicated in

Also, the bit reversing unit **1520** may be used, which reverses only a specific bit value indicated in **217**. The bit reversing unit **1520** indicated in **1540** shown in

With such a conversion, it is possible to create the key modification unit indicated in **1500**.

Also, though the present embodiment uses the structure shown in

Furthermore, the sizes of the plain text and the ciphertext are set to 64-bit, the size of the encryption key is 128-bit and the size of the expansion key is 64-bit in the present embodiment, but they are not limited to these data sizes. Also, the number of stages for the data conversion process in the data scrambling unit **1** indicated in

In addition, though the exclusive-OR operation unit **211** of the key conversion unit indicated in **211** has a configuration to execute the exclusive-OR operation to at least two of discretional part data obtained from 128 bits of concatenated first˜fourth input data X**0**˜X**3**, it can be any configuration.

Moreover, the exclusive-OR operation unit **213** executes the exclusive-OR operation between the data B substituted and converted by the data substituting unit **212** and one of the first˜fourth input data X**0**˜X**3**, it is not limited to this structure. The exclusive-OR operation unit **213** may have a configuration to execute the exclusive-OR operation between the data B and at least one of discretional part data obtained from the 128 bits of concatenated first˜fourth input data X**0**˜X**3**.

Additionally, the exclusive-OR operation units **211**, **213**˜**215** use the exclusive-OR operation as a method for combining data, but it can be any process as long as it is a process that calculates one output data from two or more input data such as addition, subtraction and multiplication.

**1700** may contain the decryption device **1200** shown in **1702**. Because this authentication process can be executed at high speed, it can reduce time actually taken from insertion of the DVD **1702** to reproduction of contents of the DVD **1702**.

As clarified from the above explanation, rather than using the method in the first related art in which the expansion key generating process and the process for getting an input for the subsequent expansion key generating process are executed by sharing a part of the same processing circuit, the processes in the encryption system related to the present invention are separated into the expansion key calculation unit and the output calculation unit, and executed.

The expansion key calculation unit combines plural data, and calculates an expansion key. The output calculation unit uses a data rotation process that can convert a process, which is repeated n times (n is a natural number), to a simple equivalent process. In this way, the overhead process at the time of decryption does not get so much bigger than the process at the time of encryption like the first related art. Therefore, it is possible that the time taken for the decryption process does not have so much difference from the time taken for the encryption process.

The expansion key calculation unit uses a complicated process of a non-linear substituting process combined with a data combining process through a substitution table, rather than a simple bit replacing process like the second related art. Accordingly, the non-linear process using the substitution table has an influence on all of the expansion keys. Further, besides when the encryption key is changed, it has a feature where all of the expansion keys generated are affected by the change. Therefore, the present invention can realize a highly random expansion key generating process.

As mentioned above, according to the encryption system related to the present invention, the issues of the first and the second related arts can be resolved.

According to the encryption system related to the present invention, it is possible to provide an encryption process, and an authentication process and the like, which are high speed and achieve a high security level. Therefore, practical value of the present invention is extremely high when used by a system or the like, where it is required to meet high standards in terms of execution speed and security level.

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US7783037 * | Sep 20, 2004 | Aug 24, 2010 | Globalfoundries Inc. | Multi-gigabit per second computing of the rijndael inverse cipher |

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Classifications

U.S. Classification | 380/44, 380/46, 380/47 |

International Classification | H04L9/06, H04L9/00 |

Cooperative Classification | H04L2209/24, H04L9/14, H04L9/0618, H04L9/0861 |

European Classification | H04L9/06 |

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